Two-center interference in electron-impact ionization of molecular hydrogen

Fast (${E}_{0}=520\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$) electron-impact ionization of molecular hydrogen (${\mathrm{H}}_{2}$) is studied experimentally and theoretically for a resolved molecular axis angle and 10 eV ejected electron energy. Fully differential cross sections were measured using an electron-electron-ion triple coincidence experiment in which the molecular axis direction is obtained for ionic ground-state dissociation. While predictions from the standard two-wave interference model are in strong disagreement with experiment a multicenter distorted-wave method obtains much better results. This demonstrates the importance of the multicenter ionic potential for the electron emission pattern at low energy and the failure of hitherto widely used simple models which treat molecular ionization as the coherent sum of atomic ionization amplitudes.